Surgical procedures in which a cardiovascular prosthesis is implanted into a patient's blood vessel are common in treating many vascular disorders. For example, one common type of cardiovascular prosthesis is an endovascular prosthesis that is used to strengthen a blood vessel wall in the location of an aneurysm, or to open an occlusion in a blood vessel.
A typical endovascular prosthesis includes a flexible, tubular member, made of fabric or polytetrafluoroethylene (PTFE), that may be anchored with sutures or carried by one or more support structures known as stents. Generally, each stent is formed from a material having an elasticity sufficient to permit radial expansion of the stent and having a strength sufficient to prevent radial collapse or burst. Such stents are typically formed from stainless steel, titanium, Nitinol, or a suitable plastic.
A common endeavor in the field of cardiovascular prosthetics is to increase the patency rate of prostheses. Thrombosis and platelet deposition on surfaces of a cardiovascular prosthesis reduce the patency rate of the prosthesis. For example, thrombosis and platelet deposition within an endovascular prosthesis may occlude the conduit defined by the endovascular prosthesis.
Many factors contribute to thrombosis and platelet deposition on the surfaces of known cardiovascular prosthesis. The most common factors are dependent upon the material or materials forming the inner surface of the conduit of the endovascular prosthesis. Typically, thrombosis and platelet deposition begin to occlude the conduit of the endovascular prosthesis when the material or materials forming the conduit of the endovascular prosthesis are foreign to the patient's body. A thrombus begins to form on the inner surface of the conduit of the endovascular prosthesis and extends annularly about the inner surface of the conduit. Eventually, the thrombus can severely restrict blood flow through the conduit defined by the endovascular prosthesis and, if left untreated, can completely occlude the conduit.
Additionally, thrombosis and platelet deposition may occur as a result of irregularities on the inner surface of a cardiovascular prosthesis. The irregularities may be formed by the structure of an inner stent that is used to support the cardiovascular prosthesis, or may be formed by the inner surface of the flexible member used for the prosthesis.
To reduce the occurrence of thrombosis and platelet deposition, the inner surface of endovascular prosthetics may be lined with biological tissue. Lining the inner surface of endovascular prostheses with biological tissue may help to reduce thrombosis and platelet deposition by providing an established protein scaffold upon which endogenous tissue cells can readily adhere and proliferate.
Biological material is typically stabilized prior to implantation. This process of stabilization, also known as fixation or tanning, usually consists of a series of chemical steps whereby: (1) the tissue's biomechanical properties are stabilized; (2) the tissue is sterilized; and (3) the antigenicity of the tissue is reduced.